Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

916
FXUS63 KLOT 250750
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
250 AM CDT Thu Jun 25 2026

.KEY MESSAGES...

- Early morning fog to dissipate quickly after sunrise.

- Next chance of rain (and maybe a few thunderstorms) comes
  during the day Friday, with another chance of showers and
  thunderstorms Saturday night into early Sunday morning.

- First heat wave of the summer expected early next week with
  the potential for highs in the 90s and peak afternoon heat
  indices over 100 degrees.

&&

.DISCUSSION...
Issued at 250 AM CDT Thu Jun 25 2026

A surface cold front will settle south of our area today. While
primarily dry weather is anticipated across the area in the
wake of this boundary, another mid-level impulse across the
eastern Dakotas early this morning is progged to slide eastward
across southern WI this afternoon. As it does, some guidance is
insistent that some isolated shower/storm activity will develop
into this afternoon, potentially focusing along the lake breeze
boundary. It appears the best potential for this activity will
largely be to our north in WI. However, given the close
proximately, we could see a few such showers developing as far
south as far northeastern IL. Accordingly, we have opted to
maintain a low (20%) chance for a couple of isolated showers,
mainly across Lake County IL this afternoon. Otherwise,
following some early morning fog, expect partly to mostly sunny
conditions today with inland temperatures topping out in the
upper 70s to near 80. Closer to the lake, an afternoon lake
breeze will keep conditions a few degrees cooler.

Late tonight into Friday, forecast attention will be on the
next wave of surface low pressure expected to track eastward
from Plains out across the Mid-Mississippi Valley region. Model
and ensemble guidance continue to depict a decent amount of
spread with the strengthen, exact timing, and track of this
system. This appears to be tied to the degree of convective
enhancement that occurs to the parent mid-level short wave later
today into tonight across the Plains. Accordingly, this does
lend lower confidence with the extent of rainfall that falls
across northern IL on Friday. Nevertheless, we continue to
advertise 20-30% chances of rain north of I-80 Friday, with
60-70%+ chances south. Regardless of the extent of rain that
falls, the threat for thunderstorms will remain low in our area,
owing to the track of the system keeping the unstable airmass
well south of our area.

The large scale upper-level pattern will amplify through the
weekend as large upper-level trough digs into the western CONUS.
As this occurs, heat and humidity will be on the increase
across the central CONUS as a large subtropical upper-level
ridge amplifies over the mid-Mississppi Valley and lower Great
Lakes regions into early next week. As this pattern change
unfolds, a surface warm front will shift northeast into the
region Saturday night into Sunday. This may foster a period of
showers and thunderstorms Saturday night into Sunday morning
along the leading edge of the EML advecting into the region
under the building upper ridge. With conditions drying out into
Sunday afternoon, we should really begin to notice the building
heat and humidity, particularly inland from the lake, where a
lingering onshore southeast wind looks to keep things cooler
through the day. Inland temperatures are currently forecast to
top out in the upper 80s, but with dewpoints potentially
climbing into the low 70s, heat indices will make it feel like
its in the mid and upper 90s. Lakeshore areas in northeast IL
should remain cooler (upper 70s/low 80s) through Sunday.

The low-level flow looks to turn offshore by Monday, so hot and
humid conditions are expected to impact all areas (including
the lakeshore areas). Persistent upper-level ridging across the
region is forecast to keep temperatures in the 90s through at
least mid-week. Combined with high dewpoints (in the 70s), heat
indices are likely to be solidly above the 100 degree mark.
Based on the current model guidance, these values are
reasonable, but with the heart of the upper ridge progged to be
centered south toward the lower Ohio and mid-lower Mississippi
Valley it is possible that ring of fire convection currently
progged to be mostly to our north could sneak farther south or
send outflow south into parts of our area offering some reprieve
from the heat. It is too soon to tell if and when this may
occur, but it something that will need to be monitored.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 104 AM CDT Thu Jun 25 2026

Key Messages:

- Patchy fog and low clouds may be observed at some TAF sites
  tonight, and possibly again tomorrow night.

- A lake breeze will result in a northeasterly or easterly wind
  shift this afternoon or evening.


Light winds and residual moisture from earlier rainfall have
allowed patches of primarily shallow fog to develop in some
areas as of 0600Z. This fog may expand and become more dense
through the night, but incoming cirrus and some lingering flow
in the boundary layer raise questions over the extent to which
that may occur. It is also possible that some of this low-level
moisture ends up forming patchy IFR or LIFR clouds instead, but
confidence in this also is on the lower side of things. Either
way, observational trends will be monitored closely through the
night as it`s possible that some of our TAFs may need to be
amended to be steered in a more pessimistic direction.

Regardless of what happens with the fog and low cloud potential
tonight, VFR conditions are likely to prevail by mid-morning and
persist through the daytime. A lake breeze will develop and
eventually push inland during the afternoon and evening, first
resulting in a northeasterly wind shift at GYY, followed by
northeasterly or easterly wind shifts at the remaining Chicago
metro terminals in the hours that follow. Ample low-level
moisture in the marine-influenced air mass behind the lake
breeze could result in another period of low clouds and/or fog
tomorrow night, but confidence in that is fairly low this far
out.

In addition, couldn`t rule out a stray shower or two popping
along the lake breeze near ORD, MDW, or GYY this afternoon.
However, the most likely outcome at this time is that the
terminals will stay dry through the current TAF period.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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